Receiving devices or systems in a communication system may receive signals or waveforms which are distorted by interference or noise. Some of the signal distortion may be caused by narrowband interference. Narrowband interference may be interfering noise or signals which are centered about particular frequencies.
Despite such interference, a receiving device must be able to detect a signal and determine its content. For example, the performance of spread spectrum communication systems such as Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) signals are severely degraded in the presence of strong sinusoidal interference.
Receiving devices use various methods, schemes, and/or systems to remove such interference. One such method employs filters, such as a notch filter, to filter out interference from a received signal.
Notch filters remove signal energy contained in a narrow band of frequencies. A fixed frequency notch filter removes a particular narrow band of frequencies. The narrow band of frequencies removed is determined by the value of the circuit elements employed in the filter.
However, in many applications, the particular frequency of the interference is unknown and, consequently, a fixed frequency notch filter is ineffective. Therefore, a filter which adapts itself to filter out interference of unknown or varying frequency is sought.